Conventional low-pass filters are suitable for following variations in the DC component of a signal which includes parasitic oscillations. However, to do this they require time. In applications such as weighing, the DC component tends to vary rather abruptly (i.e. when a body is placed on the scale pan). It may also happen that oscillations are superposed on the DC component, either from the body being weighed (e.g. weighing babies or animals) or from the support on which the scales are mounted (e.g. scales on a delivery truck or other vehicle).
Such oscillations or vibrations may be at very low frequencies, e.g. as low as 1 Hz. If a conventional low-pass filter is used to eliminate oscillations at such frequencies, the time required for the output signal from the filter to settle down with sufficient accuracy to the DC component of the input signal applied thereto, i.e. to a value representative of the weight being weighed, becomes prohibitive.
Preferred embodiments of the present invention enable this problem to be solved by providing a new electronic measurement circuit including a low-pass filter which is particularly, but not exclusively, intended for weighing applications.